Effect of dietary administration of kynurenic acid on the activity of splenocytes of the rainbow trout (Oncorhynchus mykiss)

Abstract

Kynurenic acid (KYNA ) is a metabolite of tryptophan that an organism produces constitutively along the kynurenic pathway. This substance, known as an endogenous neuroprotectant, also demonstrates some immunotropic properties. The purpose of this research has been to determine the influence of kynurenic acid administered in feed on the proliferative activity of lymphocytes (MTT assay) and activity of phagocytic cells (RBA and PKA assays) isolated from the spleen of a rainbow trout. The experiment was conducted on 100 fish, divided into 4 groups: control, not receiving kynurenic acid, and three treatment groups which were given KYNA in feed, in the doses 2.5, 25 or 250 mg/kg of feed for 7, 14 or 28 days. The strongest effect of KYNA was observed after the shortest time of its administration. It manifested itself as a depressed proliferative response of T and B lymphocytes in the group given the highest dose of KYNA and, irrespective of the dosage, as an elevated activity of phagocytic cells. The effect weakened as the administration of KYNA continued. After 28 days of administration, the increased respiratory burst activity of phagocytic cells remained only in the group receiving the highest dose of KYNA . Another, rather unexpected effect observed on day 28 was the stimulated proliferation of T lymphocytes in the treatment with the lowest KYNA dose. The results confirm the immunotropic characteristics of kynurenic acid, as of today not investigated on a model of poikilothermic animals, which encourages further investigations into possible applications of the acid in fish therapy.